Help needed with pcb design!

pdul · 22nd August 2011, 01:00 PM

I have been living a happy life with this preamp since 93, And now I have decided to build a new one with a nice finish instead of the lab looking current one.I will very much want to base it on my old linestage which to my ears is just perfect; But looking at the old pcb, the first thing that comes to mind is decay, loose traces, a lot of repairs etc. It was originally a diy that was shown in a magazine which is no more, So getting the original layout is just not possiple.
After watching these forums for a long time,I have got the impression that laying out pcb`s comes as easy to some of you guys as burbing after drinking a beer

But for me it will be a long study of programs to even get near the target. I have changed some semis from smd to thru hole cause my eyes are not what they use to be, and it will make it more flexible for experiments in the future.
I have got permission from L. Clausen to post the schematic here.
Hope that one of you guys will swallow the bate.
Regards.
(Sorry for my rusty english)

Mooly · 22nd August 2011, 01:35 PM

How about photographing the old PCB as a starting point.

I know this isn't what you are asking... the two IC's in the diagram called "one point DC servo". Are you sure there isn't an error there. The output of each opamp is shown connected to the low impedance outputs of each main stage... the same point the servo's are shown as sampling via very high value resistors.

pdul · 22nd August 2011, 01:40 PM

it is called One point dc servo. It measures and corrects in the same point.
Works fine by the way

pdul · 22nd August 2011, 01:41 PM

And with second order filtering

Mooly · 22nd August 2011, 01:43 PM

Are you sure

Ouroboros · 22nd August 2011, 01:43 PM

The first stage seems to be a transimpedance amplifier, so the "one point servo" will attempt to keep this high-impedance amplifier output dc offset at 0V. I am less certain that the second dc-servo will acomplish the same thing, as the second stage seems to have a low impedance output.

pdul · 22nd August 2011, 01:45 PM

It is a non feedback design, So no feedback loops in the servo either

Mooly · 22nd August 2011, 01:45 PM

Quote:

Originally Posted by Ouroboros

I am less certain that the second dc-servo will acomplish the same thing, as the second stage seems to have a low impedance output.

And the opamp has a 10meg ? series output resistor...

pdul · 22nd August 2011, 01:46 PM

It has worked and been in use daily since 93

Ouroboros · 22nd August 2011, 01:48 PM

The servo design is a variant of a 'gyrator' circuit, so the effect to to provide a low-impedance load at 0Hz.

Given that the servo functions as a result of a local NFB loop, I'd be wary of saying that there's no feedback loops in the design :-)

22nd August 2011, 01:35 PM	#2
Mooly diyAudio Member Join Date: Sep 2007	How about photographing the old PCB as a starting point. I know this isn't what you are asking... the two IC's in the diagram called "one point DC servo". Are you sure there isn't an error there. The output of each opamp is shown connected to the low impedance outputs of each main stage... the same point the servo's are shown as sampling via very high value resistors. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

22nd August 2011, 01:43 PM	#5
Mooly diyAudio Member Join Date: Sep 2007	Are you sure __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

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22nd August 2011, 01:40 PM	#3
pdul diyAudio Member Join Date: Jan 2009	it is called One point dc servo. It measures and corrects in the same point. Works fine by the way

22nd August 2011, 01:41 PM	#4
pdul diyAudio Member Join Date: Jan 2009	And with second order filtering

22nd August 2011, 01:43 PM	#6
Ouroboros diyAudio Member Join Date: Dec 2003 Location: Nottingham UK	The first stage seems to be a transimpedance amplifier, so the "one point servo" will attempt to keep this high-impedance amplifier output dc offset at 0V. I am less certain that the second dc-servo will acomplish the same thing, as the second stage seems to have a low impedance output.

22nd August 2011, 01:45 PM	#7
pdul diyAudio Member Join Date: Jan 2009	It is a non feedback design, So no feedback loops in the servo either

22nd August 2011, 01:46 PM	#9
pdul diyAudio Member Join Date: Jan 2009	It has worked and been in use daily since 93

22nd August 2011, 01:48 PM	#10
Ouroboros diyAudio Member Join Date: Dec 2003 Location: Nottingham UK	The servo design is a variant of a 'gyrator' circuit, so the effect to to provide a low-impedance load at 0Hz. Given that the servo functions as a result of a local NFB loop, I'd be wary of saying that there's no feedback loops in the design :-)

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